The Tec family of non-receptor tyrosine kinases plays a central role in signalling through antigen-receptors such as the TCR, BCR and Fce receptors and are essential for T cell activation. Deletion of Itk in mice results in reduced T cell receptor (TCR)-induced proliferation and secretion of the cytokines IL-2, IL-4, IL-5, IL-10 and IFN-γ. Itk has been implicated in allergic asthma and a topic dermatitis.
Tec family kinases are also essential for B cell development and activation. Patients with mutations in Btk have a profound block in B cell development, resulting in the almost complete absence of B lymphocytes and plasma cells, severely reduced Ig levels and a profound inhibition of humoral response to recall antigens. Btk deletion in mice has a profound effect on B cell proliferation induced by anti-IgM, and inhibits immune responses to thymus-independent type II antigens.
Tec kinases also play a role in mast cell activation through the high-affinity IgE receptor (FcεRI). Itk and Btk are expressed in mast cells and are activated by FcεRI cross-linking. Btk deficient murine mast cells have reduced degranulation and decreased production of proinflammatory cytokines following FcεRI cross-linking. Btk deficiency also results in a decrease of macrophage effector functions.
The Aurora proteins are a family of three highly related serine/threonine kinases (termed Aurora-A, -B and -C) that are essential for a cell's progression through the mitotic phase of the cell cycle. Specifically Aurora-A plays a crucial role in centrosome maturation and segregation, formation of the mitotic spindle, and faithful segregation of chromosomes. Aurora-B is a chromosomal passenger protein that plays a central role in regulating the alignment of chromosomes on the meta-phase plate, in the spindle assembly checkpoint, and also in the correct completion of cytokinesis.
Overexpression of Aurora-A (Aurora-2), Aurora-B (Aurora-1) or Aurora-C has been observed in a range of human cancers including colorectal, ovarian, gastric, and invasive duct adenocarcinomas.
A number of studies have now demonstrated that depletion or inhibition of Aurora-A or -B in human cancer cell lines by siRNA, dominant negative or neutralizing antibodies, disrupts progression through mitosis with accumulation of cells with 4N DNA. In some cases, this is followed by endoreduplication and cell death.
The c-Met receptor tyrosine kinase is overexpressed in a significant percentage of human cancers and is amplified during the transition between primary tumors and metastasis. The various cancers in which c-Met is implicated include, but are not limited to, gastric adenocarcinoma, renal cancer, small cell lung carcinoma, colorectal cancer, colon cancer, prostate cancer, brain cancer, liver cancer, pancreatic cancer, and breast cancer. c-Met is also implicated in atherosclerosis, lung fibrosis, allergic disorders, autoimmune disorders, and conditions associated with organ transplantation.
Accordingly, there is a great need to develop compounds useful as inhibitors of protein kinases. In particular, it would be desirable to develop compounds that are useful as inhibitors of Tec family (e.g.,Tec, Btk, Itk/Emt/Tsk, Bmx, Txk/Rlk) and Aurora family protein kinases, as well as c-Met, particularly given the inadequate treatments currently available for the majority of the disorders implicated in their activation.